Water resource exploitation for human; needs has grown: by, leaps and bounds
in the last two decades. Nearly all the suitable sites for storage dams and river
diversions have been utilized and ground water 'extracted regardless of consequences
as in Bangkok

Water for all by the year 2000 still remains an ideal, Rivers that were once
perennial now become, raging torrents that convey their runoffs in the form of
flash flooding.. As forests are reduced by deforestation and catchments urbanised
the need to harvest rain before it reaches the dry streams beds or fall into polluted
rivers becomes of paramount importance.

Runoff areas: in catchments continue to diminish and are replaced by concrete
paving or bitumen. covered roads or asbestos or tiled roofs. Rainfall runoff from
such artificial catchments can be collected in cisterns. above ground or in tanks
below Preserving the rain close to where it fell avoids contamination that occurs
with surface runoff : Percolation and. evaporation loss °is reduced: But rainfall
in urban areas has its drawbacks when atmospheric pollution sulphur dioxide and
carbon dioxide from vehicular traffic; coal fired power stations or industrial
flue gases can convert the composition of rain to acid rain is very real.

Collection of rain in cisterns also could attract growth 'of organisms and
larvae that could promote diseases like malaria, filaria, dengue and Japanese
encephalitis, if such water is consumed without boiling. Water -stored in. underground-
cistern could be contaminated by leakage from septic tanks. in the proximity adding
nitrates and phosphorous Cisterns take up space in high value urban areas.

Population growth the world over has mushroomed to such extents that efforts
made by countries to supply their basic requirements of water for drinking;. for
'irrigation and for power production can hardly copy with.